Needless to say, resin-made shaped products are adopted for a wide variety of uses in modern societies. In case where required properties are not satisfied with a single resin, laminar or laminated products of plural resins have been used. Among these, resin-made bottles are used widely and in large masses as containers for various liquid materials, such as drinking water, seasonings, edible oil, alcoholic beverages, fuels, and detergents, because of their lightness, transparency allowing seeing therethrough of the content materials, etc. This particularly holds true with so-called “PET bottles” made of polyester resins, especially bottles made of PET (polyethylene terephthalate).
However, in view of town problems nowadays including the demands for reducing the load to the environment and reducing the garbage, the recycling of such resin-made products, particularly bottles, used in large masses has been demanded. As for the manner of recycling, various types are present, including a heat energy recovery type through combustion, a chemical recycle type of recycling to monomers, a starting material type of recycling to a starting resin material through pulverization and refining steps, and a returnable type for re-utilization as bottles. In the case of PET bottles among others, the starting material-type of recycling to the starting resin material through pulverization and refining steps is frequently adopted, and the recovered resin material is re-utilized for producing fiber products, etc., in many cases.
On the other hand, nowadays, also bottles are required to suppress the transmission therethrough of carbon dioxide gas or oxygen gas for improving the preservability of contents therein. For achieving the improvement, there has been proposed, e.g., a multiple layer structure of providing a gas barrier coating or disposing a gas barrier resin layer as an intermediate layer. This requirement is particularly critical for bottles having a volume of 500 ml or less.
In the case of a PET bottle provided with a multiple layer structure by disposing a gas barrier coating or an intermediate gas barrier resin layer, it is possible that the quality or safety of the recycled resin materials is questioned if it is difficult to sufficiently separate the PET resin material and other resin materials.
Further, it has been also tried to use colored PET bottles in order to prevent photodegradation of contents, such as beer, or achieve a design effect, but the utilization thereof has been restricted because it is liable to make difficult the recycling due to the problem of color mixing of the recycled resins.